If you’re printing maps yourself (like you should be with great free software like Caltopo), you know the importance of protecting them from the weather. Most of the time, if you print maps on a color laser printer and keep them in a 1 gallon Ziploc freezer bag, that's going to be good enough.
(Besides maps, another excellent thing to print on waterproof paper is a SOAP note for your first aid kit.)
But in in challenging conditions, you may want to take some extra steps for durability. That's when you might want to consider waterproof paper.
“Rite in the Rain” paper, is a fine choice and has been around forever. The one downside is it can tear. It costs about $18 for 50 sheets, or about $0.36 a sheet. If you want to experiment with waterproof paper, this is a low-cost option to get started.
The next step up in waterproof paper is a type which is actually a sort of plastic, that takes color laser printing beautifully, basically tear proof, and complete waterproof.
How tearproof and waterproof? Watch the first 45 seconds of ths video to get an idea.
The downside of this paper is that it’s expensive (about $40 for 50 sheets, or $.80 per sheet.) But, if you only use it for maps where you really need the extra durability, such as maybe for canyoneering, ski touring in a storm, sea kayaking, or a longer mountaineering trip when you really need your map to last, it could be well worth it.
There are a few different flavors on Amazon. I have a box of the “iGage” paper. When I want to print maps, I make them in Caltopo, save them as a PDF file, put them on a USB drive, take that to the local FedEx store, put a few sheets of my waterproof paper in the top of tray #1, and print my maps as normal.
Disclaimer, this paper is made of a kind of plastic, and it's conceivable that it could jam or melt or do something weird in certain kinds of laser printers. If you do this at FedEx store, you may want to ask an employee if it's OK to use. Personally I've done it many times and never had a problem, your mileage may vary.